1. Field of the Invention
The present invention generally relates to medical devices, and in particular, to an improved balloon catheter and method of manufacture.
2. Description of the Related Art
Medical balloon catheters have been proven efficacious in treating a wide variety of blood vessel disorders. Moreover, these types of catheters have permitted clinicians to treat disorders with minimally invasive procedures that, in the past, would have required complex and perhaps life threatening surgeries. For example, balloon angioplasty is now a common procedure to alleviate stenotic lesions (i.e., clogged arteries) in blood vessels, thereby reducing the need for heart bypass operations.
Compliant inflatable balloons, of the type used with medical catheters, increase in diameter with increasing inflation pressure until the balloon burst pressure is reached, as is well-known to those of skill in the art. Such balloons are especially advantageous when used as a medical catheter balloon, or as the securing element of an anchorable guidewire. In both applications, the balloon must be expanded to contact the blood vessel wall. In some treatment procedures, however, the clinician does not know the precise diameter of the blood vessel segment that the balloon must contact. In these situations, the compliant expansion profile of the balloon permits the clinician to make the required contact, by application of increasing inflation pressures to cause increased balloon radial expansion until contact is achieved.
Conventional compliant expansion balloons are generally made of elastomeric materials, such as latex and silicone. Balloons made of these materials utilizing conventional balloon formation techniques suffer from several disadvantages which adversely affect the balloon's performance.
One disadvantage of conventional compliant balloons relates to their elastic response. It is desirable for catheter balloons to have a predictable inflation profile. That is, the balloon should inflate to a certain known size upon application of a specific pressure. Moreover, the balloon should exhibit good elasticity, inflating to approximately the same size upon application of the same specific pressure or volume, even after the balloon has been inflated and deflated multiple times. However, conventional compliant balloons often do not exhibit this desired elastic response, and tend to inflate to larger sizes upon application of the same specific pressure each subsequent time they are inflated. This is because each inflation stretches the balloon, and upon deflation, the balloon does not return to its original deflated size, but instead is somewhat larger. Consequently, upon each subsequent inflation, the stretched balloon inflates to a larger size than before, making it difficult for the clinician to predict the amount of pressure that must be applied to inflate the balloon to the size needed to contact the vessel.
Another disadvantage of conventional compliant balloons relates to their longitudinal expansion. As described previously, compliant balloons tend to increase in radial diameter with increasing inflation pressure. In addition, many compliant expansion balloons also tend to increase in length with increasing inflation pressure. This is an undesirable expansion characteristic, as it creates an unwanted shearing force within the blood vessel, which could lead to vessel trauma.
Accordingly, there exists a need for compliant expansion balloons for use on medical catheters, or as securing members on anchorable guidewires, which have a predictable elastic response, a predictable longitudinal expansion, and a predictable diameter, at different volumes or pressures. In addition, there is a need for methods of making such balloons.
Balloons used for angioplasty and other procedures are bonded to catheter tubular bodies. Conventional balloon bonding techniques used to mount the balloons to catheter tubular bodies include adhesive bonding and heat bonding, as known to those of skill in the art. When adhesive bonding is used, each end of the balloon is mounted to the catheter tubular body to form a fluid tight seal. An adhesive is applied to the ends of the balloon which wicks into the balloon to form a seal with the catheter tube. Typically, clamps are placed adjacent to the working area (i.e., the area within the balloon which is not bonded to the catheter and which is therefore available for inflation) to prevent adhesive flow into the working area. This technique, however, does not provide complete control of the working length because clamps are not completely effective in preventing adhesive flow into the working area. In particular, the difficulty in controlling the clamping force may allow the adhesive to wick into the working area. This creates the problems that the balloon working length may not be at the precise location desired on the catheter tubular body, and that balloon inflation may not be uniform. Thus, there is a need to control adhesive wicking of the balloon seal to control the balloon working length.
A further problem arises from the need to inflate the balloon in a uniform manner. The balloon must be centered around the catheter tube in order to allow a more uniform vessel occlusion or similar effect. Thus, there is also a need for a balloon catheter and a method for manufacturing the same wherein a balloon is centered around a catheter to allow uniform inflation of the balloon.